Intraocular lenses (IOLs) are implanted in patients' eyes either to replace a patient's lens or, in the case of a phakic IOL, to complement the patient's lens. Some conventional IOLs are single focal length IOLs, while others are multifocal IOLs. Single focal length IOLs have a single focal length or single power. Objects at the focal length from the eye/IOL are in focus, while objects nearer or further away may be out of focus. Multifocal IOLs, on the other hand, have at least two focal lengths. For example, a bifocal IOL has two focal lengths for improving focus in two ranges: a far region corresponding to a longer focal length and a near region corresponding to a shorter focal length. A trifocal IOL has three focal lengths corresponding to a near region, an intermediate region and a far region. Other multifocal lenses may have another number of focal lengths
To provide multiple focal lengths, multifocal IOLs typically divide the lens into zones (e.g. annular regions) based upon the distance from the center of the lens. One or more zones near the center of the lens are configured for near vision. The zones farther from the center of the lens are configured for far vision. For example, some conventional IOLs may utilize diffraction to provide multiple focal lengths. Diffractive IOLs utilize a diffraction grating formed on a base curve on the surface of the IOL. The base curve corresponds to the radius of curvature for the lens. The diffraction grating typically takes the form of microscopic echelettes, or surface saw-tooth like facets, formed on the lens surface. The echelettes form a diffraction grating having a particular focal length. Each zone includes a set of echelettes having a particular step height and radius of curvature. Zone(s) closer to the center of the lens may have echelettes configured for a shorter focal length and may be dedicated to near vision. Zones closer to the edge of the lens may have echelettes configured for a longer focal length and may be dedicated to far vision.
In addition, the zones may also be apodized to reduce artifacts such as glare or halos. Apodization decreases the step heights of the echelettes with increasing distance from the center of the lens. In addition to zones further from the center being dedicated to far vision, therefore, the step heights of the echelettes for these zones are shorter.
Although the conventional diffractive IOLs function acceptably well in most patients, further improvements are desired. For example, patients may not only require different corrective powers, but the physical characteristics of the patients' eyes may also differ. For example, patients having eye geometries that vary from the norm may have limited success with a particular IOL. Accordingly, what is needed is a system and method for improving the performance of IOLs for a variety of patients.